The scope of this study was to evaluate the impact of the main environmental gradients on the distribution of benthic species of the Greek waters. In addition, we re-examine the baselines of benthic ecology regarding the community structure and species succession along an environmental stressor.
Through our work we highlight the importance of the species geographic positions along the main environmental gradients which shape the species responses. The benthic communities of this study presented various responses unlike the traditional approach which is based on the use of relevant benthic indices. The benthic communities of the Aegean Sea were defined by the environmental gradients of salinity, temperature and primary productivity found in these marine region. Diversity was significantly lower in areas that are characterised by upper and lower extremes of the environmental values. Consequently, increased diversity was documented in areas characterised by mild environmental disturbance. This is attributed to the fact that marine areas with reduced environmental stress, functionally different species co-occur due to their ecological differences which allow the use of different sources and sediment position.
Based on traditional approaches, the coastal benthic communities of the Aegean Sea did not reflect the water column ecological status in terms of eutrophication. However, a species-level approach rendered valuable insights regarding the environmental status of the water column. More specifically, through this work’s proposed methodology, the bivalve distribution responded accordingly to the water column chlorophyll – a concentration. The main approach in this work was consisted by two steps: The first step was to identify the indicator species of a specific habitat and the second step was to incorporate them in relevant
Species Distribution Modelling Methods in order to identify their habitat suitability. The tolerant species Corbula gibba (Olivi, 1792) was the indicator species of the eutrophic areas of this study and the habitat suitability derived from the modelling process reflected the overall eutrophication status. Accordingly, the sensitive species Flexopecten hyalinus (Poli, 1795) was the indicator species of pristine areas with minimum environmental disturbance in terms of chlorophyll concentration. Based on the mentioned methodology, the relevance of the present ecological classes of the benthic species was evaluated under the scope of climate change. For this aim we also used the sensitive species Moerella donacina (Linnaeus, 1758) and the tolerant species Abra prismatica (Montagu, 1808). Based on the findings of this study, an overall reduction of the distribution was observed for the tolerant species when projected under the RCP8.5 for the year 2100. The species Moerella donacina is expected to retain the main part of its habitats under the increase of ~ 3 ˚C while an overall geographic expansion is expected for the sensitive species Flexopecten hyalinus. According to our findings, the species responses to climate change (or any other environmental stressor) depends on their climatic suite that shapes their niche regardless of their present disturbance classification (sensitive or tolerant).
Our initial hypothesis regarding the use of indicator species as proxies of environmental disturbance is met. Through our work, we highlight the use of benthic indicator species as biotic tools for assessing the effects of various stressors such as eutrophication and climate change on marine ecosystems. Additionally, we suggest the use of ecological niche as a suitable metric to assess the tolerance of a species to an environmental stressor. The habitat suitability models represent an important alternative in marine health assessment rendering accurate results much faster than the traditional methods used in benthic ecology.